Gas sensor assembly and method

ABSTRACT

A gas sensor assembly comprises a housing ( 65 ) including a bore ( 61 ). A pin ( 50 ) extends through the bore ( 61 ) and an O-ring ( 100 ) is located in the bore. The O-ring ( 100 ) contacts the pin ( 50 ) and parts of the bore ( 61 ) so as to be restrained against movement in both lateral and axial directions. Two- and three-shot molding processes are described for fabricating the assembly.

This application is a 371 of PCT/GB01/01862 filed Apr. 26, 2001. Thisapplication claims priority from UK Application 0010180.8, filed Apr.26, 2000.

The invention relates to a gas sensor assembly and a method formanufacturing a seal assembly for a gas sensor assembly.

BACKGROUND OF THE INVENTION

There are a variety of gas sensor constructions in which it is necessaryto seal a member such as a pin or the like into a bore so as to preventthe passage of liquid or gas through the bore. O-rings have been used inthe past to achieve such sealing both in cases where the components moverelative to one another (such as described in U.S. Pat. No. 4,221,651)and in which they are relatively static. The present invention isconcerned with a static arrangement of components.

The method of securing O-rings in a static sealing configurationrecommended by manufacturers is to place the ring in a U-shaped recessextending around the bore so that the ring contacts the elongate memberand the seal action is based on the ability of the seal to undergo axialor radial deformation of its cross-section. In order for the seal tofunction properly, manufacturers require that the size of the groove orchannel is larger than the O-ring cross-section typically having across-sectional area more than 25% that of the O-ring so that thepressure can act on a relatively large part of the ring surface and sothat there is sufficient space in the groove should any volume increaseof the O-ring occur due to exposure to chemicals.

We have found, however, that some leakage of liquid still occurs inthese configurations.

BRIEF SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, a gas sensorassembly comprises a housing containing gas sensing components; a membersecured to the housing; and an annular seal supported by the housing incontact with the member and parts of the housing so as to be restrainedagainst movement in both lateral and both axial directions.

We have undergone detailed investigations into the use of annular sealssuch as O-rings in these static situations and we have realized that oneproblem that can occur in certain applications is that if the fluidpressure reduces, then the seal will relax to an extent dependent uponthe elastic properties of the material. Furthermore, in certainapplications such as electrochemical gas sensors, there may well be nopressure exerted by the retained liquid (the electrolyte). However, byvirtue of the nature of the assembly, the joints between the matingsurfaces act as capillary channels allowing the liquid to wick up intothe seal area. Thus, the region around the seal quickly becomes bathedin liquid such as acid under conditions where the seal itself is notnecessarily under compression. Thus, the possibility of leakage isincreased.

Our solution is to ensure that the seal is restrained on all four sidesand is preferably stressed or always under compression whatever thefluid pressure and thus the seal condition is maintained.

The invention can be used in a wide variety of situations in which sealsagainst gases and/or liquids are required. It is particularly usefulwhere the member is an electrical connector located in a bore but isalso applicable to seal other components such as a gas filter top.

In addition, the invention is applicable to a wide variety of gassensors such as electrochemical, pellistor, infrared or calorimetric gassensors. For example, infrared devices have O-rings around their gaschambers, and calorimetric sensors with two part housings which cliptogether, to restrain a filter membrane via an O-ring. Pellistorhousings involving O-ring seals are also known.

The invention is of particular benefit when used with an electrochemicalgas sensor of the kind comprising sensing and counter electrodes andintervening electrolyte located within a housing. The electrodes areelectrically connected to respective connectors extending through boresin the housing to which they are sealed.

The connectors provide an electrical connection between (a) the internalelectrode and associated current collection means and (b) the externalcircuit where the sensor output is measured and processed. Additionally,such connectors may be used to allow potentiostatic control of thesensor electrode operating potential via appropriate circuits.Connectors used in this application require relatively high conductivity(to limit any IR losses between the sensor and theindicating/controlling circuitry). Suitable materials include platinumand gold, often in the form of coatings on nickel or steel components,graphite (in rod form), and metal coated and/or plated polymerics.

These connector components may be in the form of, for example, pins,pads, wires, ribbons, etc.

An important aspect in the construction of these sensors is theprevention of leakage of electrolyte. This is particularly important inthe case of oxygen sensors which employ liquid electrolyte, usually inthe form of strongly alkaline liquid. Any minor defect in the sensorrepresents a potential leakage path. In particular, it is well knownthat the electrical connections through the housing are frequently thesources of electrolyte leakage.

In comparatively large sensors where minimisation of internal volume isnot a primary design requirement, it is common to incorporate adouble-walled construction method, so that the connectors pass throughthe sensor body in a region which is already isolated from theelectrolyte reservoir. Under such circumstances, the constraints placedupon the connector/body seal, whilst significant, are relatively easilymanaged.

However, in sensors where internal volume is at a great premium (forexample in metal-air oxygen sensors where the device lifetime isfundamentally dictated by the volume of consumable lead incorporated),it is generally not possible to employ a double-walled method ofconstruction. In these circumstances, the longevity and reliability ofthe connector/body seal are critical.

A typical example of a known construction makes use of a connector pinwhich passes through a moulded polymer sensor housing in an areacontaining an aggressive liquid electrolyte (which may be an acid oralkaline material). Current design and production methods usually relyon the interference fit of the connector into the housing in order toprovide both mechanical fixation and an hermetic seal, therebypreventing the transport or migration of electrolyte from within thesensor body (i.e. leakage).

The main shortcomings of this technique are that due to

-   -   strain acceptance limits,    -   differing coefficients of thermal expansion,    -   the effect of mould processing upon the polymer characteristics,        and    -   ageing characteristics of the differing materials involved        (leading to creep),        the properties of the hermetic seal are not consistent.        Therefore, leakage is generally not particularly well controlled        and may cause premature cell failure and/or external        contamination with electrolyte.

In other examples, a barb can be added to the pin to assist in itsretention once the initial insertion has been made. This can beimportant where, for example, the pin is pushed into and removed fromsockets on connector boards which might tend to withdraw the pin fromthe sensor itself. As one increases the size of the barbs beyond thatwhich can be readily forced through a given bore, it is also a naturalstep to utilize “hot insertion” processes, where thermal and/orultrasonic methods (for example) are used to cause local heating of thesensor housing which then cools and re-seals around the pin and barb.However, none of these additional steps are in themselves sufficient toguarantee leakproof seals.

Consequently, the invention is particularly suited to overcome theseproblems with electrochemical gas sensors.

In some cases, the annular seal is unstressed but in the preferredarrangement the seal is stressed in at least one and preferably alllateral and axial directions.

The annular seal may be made of (natural) rubber but can advantageouslyemploy a wide range of suitably compliant materials. In variouscircumstances, silicones, (thermoplastic) elastomers, polymers, PTFE,soft metals etc. might all be selected on the grounds of particularproperties (e.g. chemical resistance, deformability, temperaturebehaviour, etc.).

The seal is typically an O-ring, either of the conventional type havinga circular cross-section when relaxed or a non-circular cross-section asdescribed below.

Additional sealing may be achieved by utilizing a cured potting compoundcompatible with the fluid to be used, the housing and elongate membermaterials.

We have found that using a suitable potting material, particularly if itis thermally or optically, eg UV, curable, significantly increases theintegrity of the seal.

This aspect of the invention, however, is applicable to any pottingcompound with properties which render it physically (e.g. throughthermal expansion etc. ) and chemically (i.e. resistant to attack, notcorrosive) compatible with the liquid, elongate member and housingmaterials. Sealing on the outside of the housing is preferably employed,but in principle this could also (or alternatively) be done inside thehousing. Although shadowing may be a problem in the case of light-curedmaterials, photoinitiated cationic compounds, where light is used tocommence the reaction which then proceeds unaided, are now beingconsidered for such applications. These do not suffer from significantshadowing.

In electrochemical gas sensors, the use of gelled electrolyte in placeof a liquid has been proposed to further reduce the risk of electrolyteleakage. In such cases, the electrolyte is immobilised within a suitablegelling agent in order to reduce the free liquid volume within thecasing.

The gelling reaction may take place in situ i.e. by placing thereactants in the housing and then running the entire assembly through anappropriate thermal curing cycle. However, some ungelled liquid tends toremain within the sensor, and the whole sensor assembly is subjected tothermal stresses which are typically at the extremes of the recommendedoperating range and may even be outside the specified operatingconditions. The use of “pre-gelled” electrolyte, which is mixed with thegelling agent prior to introduction into the sensor minimizes the freeliquid volume and obviates the need for thermal cycling of the sensorhardware.

However, experience shows that the use of gel does not allow anycompromise in the efforts taken to provide good seals in regions wherethe electrolyte comes into contact with members passing through thesensor body. Indeed, given the requirement for equally robust sealsirrespective of the presence or absence of gelling agents, sensormanufacturing processes may actually be simplified by using liquidelectrolytes. All these options are open to the sensor designer.

Another reason why leakage can occur in seal assemblies of this type isdue to the number of components involved and therefore we provide inaccordance with a second aspect of the present invention, a method ofmanufacturing a seal assembly for a gas sensor assembly, the sealassembly comprising a housing to which a member is secured in use; andan annular seal supported by the housing, the method comprising mouldingthe housing and seal in separate injection moulding shots, such that theseal contacts the member in use so as to seal the bore against thepassage of fluid.

In this aspect of the invention, instead of providing the seal as aseparate component, it is pre-moulded into the housing. Thus, thecomponent count is being reduced which not only assists in reducing theleakage problem but also simplifies assembly. As with the first aspectof the present invention, preferably the seal is located in an annular,generally U-shaped recess opening into the housing and contacts opposedsides of the recess and the side of the recess opposite the member. Theterm “U-shaped” is to be read broadly and to include laterally openingrecesses being a variety of cross-sections such as square, rectangular,hyperbolic, etc.

Most preferably, the seal is stressed in at least one, preferably all,lateral and axial directions.

A further advantage of this method is that the seal may be chemicallybonded to the housing thus significantly improving the seal and avoidingcapillary leakage. Some overall compression of the seal is generallydesirable which, where the seal surrounds a bore, could be achieved byproviding the seal slightly proud of the bore. However, this compressionis likely to be significantly less than that required to form aconventional seal in order to provide the required integrity.

Typically, the housing is moulded before the seal. However, in analternative approach, the seal is moulded around the member in a firstshot; and the housing is moulded around the seal and member in a secondshot.

Furthermore, in accordance with a third aspect of the present invention,we provide a method of manufacturing a seal assembly for a gas sensorassembly, the seal assembly comprising a housing to which a member issecured in use, and an annular seal supported by the housing, the methodcomprising injection moulding the housing about the seal.

For example, a sensor housing could be moulded around a free standing,annular seal.

The method can be extended when the member is elongate and sealed in abore of the housing to a three shot process in which in a third shot anadditional seal is moulded into the bore.

The same or different, usually plastics, materials may be used in eachmoulding shot. Typically, the seal is fabricated from a thermoplasticelastomer (TPE) while the housing is made from another polymer.

The use of two-shot moulding/TPEs allows the generation of a separateseal via radial compression of the TPE. The use of a three-shot mouldingtechnique offers additional benefits by virtue of the fact that someTPEs offer favorable sealing properties to metals (e.g. a pin connector)whereas others are to be preferred for use on polymer surfaces. Thus, athree-shot moulding method potentially allows a complex seal to befabricated using a sandwich or layered structure where, in the case ofan electrochemical gas sensor, the critical electrolyte seal isfabricated using materials optimised for the contacting surfaces.

The moulded seal is typically in the form of an O-ring but other formsof seal may be used. Seals with a variety of more complex footprints(e.g. a car head gasket) and cross-sectional forms (e.g. “lobed” O-ringsor “wiping” seals) could be used.

It will be appreciated that the invention is applicable to two, three,four or more electrode electrochemical gas sensors. Furthermore,typically the housing will provide controlled gas access to the sensingelectrode, for example by incorporating a gas phase, Knudsen, or solidstate diffusion barrier.

Some examples of electrochemical gas sensors and methods for theirassembly according to the present invention will now be described withreference to the accompanying drawings, in which:—

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an exploded view of a sensor assembly;

FIG. 2 is a cross-section through part of the housing of the sensorshown in FIG. 1;

FIGS. 3A-3D are partial, perspective views of different stages in thefabrication of part of a gas sensor using a two-shot injection mouldingprocess;

FIGS. 4A-4D are perspective views of part of another example of anelectrochemical gas sensor housing during its fabrication using atwo-shot injection moulding process;

FIGS. 5A-5D are perspective views illustrating the fabrication of partof a further example of an electrochemical gas sensor using a three-shotinjection moulding process; and,

FIG. 6 illustrates cross-sections through four alternative annularseals.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates the primary components of a sensor assembly includinga main housing component 65 which, following assembly, is bonded bywelding or the like to a top housing component 2. The top housingcomponent includes a central capillary hole 4 extending through it(which forms a gas phase diffusion barrier), a filter 5 being located inalignment with the hole 4. A sensing electrode 6 is located below thecapillary hole 4. Below the sensing electrode 6 is a separator 7 and anO-ring 8. A counter electrode in the form of a lead anode 9 ispositioned beneath the O-ring 8 and sits on a floor seal 10. It will beappreciated that several components have been omitted from FIG. 1 forclarity and indeed the construction of the assembly shown in FIG. 1 isconventional apart from the pin mountings which are to be describedbelow.

The sensing electrode 6 and the counter electrode 9 are each connectedto respective conductors (not shown) which are in turn connected torespective pins 50 which protrude through holes 61 in the base of thehousing component 65. As will be described in more detail below, thepins 50 are secured in the holes 61 partly by a friction fit and partlyby epoxy potting material 20. They are also sealed to the holes 61 viaO-rings 100.

A dummy pin 40 extends from the base of the housing component 65 toassist in locating the sensor on a support member.

FIG. 2 illustrates an example of the invention in which a T-shapedconnector pin 50 is secured in a widened part 60 of the bore 61extending through the base of the housing component 65. This securementis achieved partly by means of an interference fit between a lateralflange 62 integrally formed with the rest of the pin 50 with the surfaceof the bore 60 and partly by means of a potting material 20 which fillspart of the space within the widened part of the bore 60. Afterinserting the pin 50 into the bore 61, the widened part of the bore 60is filled with the potting material, such as an epoxy, which is thencured under UV radiation.

The electrolyte reservoir 66 defined by the housing part 65 is thenprovided with a consumable lead anode 67 which is saturated inelectrolyte. This could be in liquid form, in which case it will belargely wicked into the compressed body of the lead wool ball bycapillary action but with the possibility of some seepage of liquid.Alternatively, the electrolyte might be either pre- or post-gelled, inwhich case it would be more robustly held within the cavities formed bythe intertwined strands of lead wool. The pre-gelled electrolyte is aliquid electrolyte with suitable additives that cause the material to“gel” by application of heat, thus reducing the amount of free liquid bya significant degree. The electrolyte is “gelled” in the lead anode 9prior to assembly of the anode into the sensor to minimise both heatcycle stresses on the sensor, and the free liquid electrolyte inside thesensors.

The polymer preferably, although not exclusively, comprises unitsderived from polyacrylamides as is known in the art.

Primary leakage control is achieved by sealing the pins 50 to thehousing by means of O-rings. As can be seen in the example of FIG. 2 theinternal end of each pin 50 is surrounded by an O-ring 100.

The O-ring 100 is made of rubber and as can be seen in FIG. 2 iscompressed in both lateral and axial directions. Axial constraint isprovided by an axially facing shoulder 70 of the widened part 61 of thebore 60 and by an axially upwardly facing surface 71 of the flange 62.Lateral constraint is provided by a laterally outwardly facing surface72 of the pin 50 and a laterally inwardly facing surface 73 of thewidened part of the bore 60.

The unconstrained and unstressed form of the O-ring is shown in dottedlines in FIG. 2. It can be seen, therefore, that the O-ring is stressedand consequently leakage of electrolyte through the bore 61 is minimizedeven with variations in temperature and liquid pressure and otherphysical conditions since the O-ring remains in its stressed condition.The exact position of the O-ring 100 can be varied and for example itcould be located downstream of the interference fit as opposed toupstream as shown in FIG. 2.

In the FIG. 2 example, the various components forming the seal assemblyare separately manufactured and then connected together.

We have found that significant advantages can be achieved using atwo-shot or three-shot injection moulding process.

FIG. 3A illustrates part of a main housing moulding 120 similar to thehousing 65 in FIG. 1. The housing moulding 120 is formed in a singleinjection moulding shot and includes a base 125, a dummy pin 40 and abore 130 having a narrow section 131 and a widened section 132. The bore130 can be seen more clearly in FIG. 3B.

In a second injection moulding shot, a thermoplastic O-ring 135 islocated in the base of the widened part 132 of the bore 130 to which itis both mechanically and chemically bonded (FIG. 3C). This produces asemi-constrained form of the seal which becomes fully constrained uponthe introduction of a metal pin 140 (FIG. 3D) generating a seal betweenthe pin and main polymer housing. The pin 140 is retained in position bya radial barb 145 as in the FIG. 2 example.

FIG. 4 illustrates an advantageous development of the FIG. 3 example. Inthis case, the bore 130 includes a radial flange 150 produced during thefirst moulding shot (FIG. 4A), the flange 150 having a central opening155. In a second shot, a seal 135 is injected into the space definedbetween the flange 150 and the base 160 of the widened part 132 of thebore 130. In this design, the seal 135 is pre-constrained by this spaceinto which it is moulded, again achieving both mechanical and chemicalbonding to the base housing polymer. This means that the pin will alwaysbe fitted (FIGS. 4C and 4D) to a defined position therefore reducing thedegree of variability in seal compression. In effect, the space in whichthe seal 135 is located defines a U-shaped recess surrounding the bore.

FIG. 5 illustrates a further development of the moulding process inwhich a three-shot process is used. Initially, a metal pin 140 isprovided (FIG. 5A) as in the previous examples. This is loaded intomould tooling (not shown) and then in a first shot, a seal 160 ismoulded around a flange 144 defining the barb 145 (FIG. 5B).

In a second shot (FIG. 5C), the main body of the housing 120 isinjection moulded about the pin and seal thus defining the bore 130.

Finally, in a third shot (FIG. 5D), an external seal is moulded as shownat 170.

A variety of materials may be used for the different componentsproviding they are compatible with each other and Table 1 below providesa list of thermoplastic materials and an indication of where they arecompatible for good adhesion.

Typically, the housing 120 will be moulded from a polymer plasticsmaterial such as ABS while the seals 160,170 will be formed fromthermoplastic elastomer materials (TPEs) or high flow polymers of whichsuitable examples are set out in Table 1.

It will be appreciated that the FIG. 4 example could be modified suchthat in the first shot the seal 135 is moulded around the pin 140 andthen the housing 120 is moulded around the seal in a similar way to thesteps illustrated in FIGS. 5A-5C.

The two- and three-shot moulding processes are preferably carried outusing a single tool although this is not essential.

Whilst the designs discussed above relate to the manufacture of anoxygen sensor, the design is not limited to sealing in the region ofcurrent collectors. Neither is it limited to oxygen sensors, but canalso be used to generate the seals within any other areas of the gassensor including toxic sensors, and indeed wherever an O-ring iscurrently employed.

In addition, although the examples described above make use ofconventional O-rings with circular cross-sections, a variety of otherannular seals could be used. FIG. 6 illustrates cross-sections throughfour such examples which illustrate the wide variety of cross-sectionsapplicable.

TABLE 1 Typical material adhesion combinations Thermoplastics MaterialPPO Premolding ABS ASA CA EVA PA 6 PA 66 PC PE-HD PE-LD PMMA POM PP MODPS-GP PS-HI PBTP TPU Ther- ABS + + + + + + + − − + − − − ∘ ∘ + + moplas-ASA + + + + + + + − − + − − − ∘ − + + tics CA + + + ∘ − − − − − − − + +EVA + + ∘ + + + + + + PA 6 + + + + + ∘ ∘ − ∘ − − − + + PA 66 + + + + ∘ ∘∘ − − − − − + + PC + + + ∘ + − − − − − − − + + PE-HD − − − + ∘ ∘ − + + ∘∘ − − − − − — PE-LD − − − + ∘ ∘ − + + ∘ ∘ + − ∘ − − − PMMA + + ∘ ∘ + ∘ −− − − POM − − − − − − ∘ ∘ + − − − − − PP − − − + ∘ − − − + ∘ − + − − − −− PPO − − − − − − − − − − − + + + − − MOD PPO − − − − − − − − − −− + + + − − MOD GTX PS-HI ∘ − − + − − − − − − − − + + + − −PBTP + + + + + + − − − − − − − − + + TPU + + + + + + − − − − − − + +PVC-W + + + − − − + − − − − + + SAN + + + + + + + − − + − − ∘ − − + TPR∘ ∘ − − − − ∘ ∘ + + − ∘ − PETP + + + − − − − − − − + PEI PSU + + + − − −− − − + BLEND + + + + + − − + − − − − − + + PC-PBTP BLEND + + + + + −− + − − − − − + + PC-ABS TPE PP/EPDM Elast- EPDM mer NR SBR LSRThermoplastics Rigid/flexible bonds BLEND BLEND TPE Material PC- PC- PP/Elastomers Premolding PVC-W SAN TPR PETP PEI PSU PBTP ABS SEBS TPU EPDMEPDM NR SBR LSR Ther- ABS + + ∘ + + + + + + moplas- ASA + + ∘ + + + + +tics CA + + − EVA − + PA 6 + − + + + + + − PA 66 + − + + + + + − PC +− + + + + + + PE-HD − − ∘ − − − − PE-LD − − ∘ − − − − PMMA + + − + + +POM − − − − PP − − + − − − + − + PPO − ∘ + − − − − MOD PPO − ∘ + − − − −MOD GTX PS-HI − − ∘ − − − − ∘ PBTP + + − + + + + + TPU + + − + + +PVC-W + + + + SAN + + + + + TPR + − − − − + PETP − + + + + ∘ PEI + − PSU− + + + + BLEND + + − + + + + + PC-PBTP BLEND + + − + + + + + PC-ABS TPEPP/EPDM + + Elast- EPDM + mer NR + SBR + LSR + + Good adhesion ∘ Badadhesion − No adhesion

1. A method of sealing a gas sensor assembly comprising a housing; andan annular seal supported by the housing and defining a bore, the methodcomprising: molding the housing and seal in separate injection mouldingshots: providing an elongate member including a laterally extendingflange, the flange having a radial barb; inserting the elongate memberinto the bore so that the annular seal contacts a surface of the flangeand an adjacent elongate portion of the member while the radial barbengages the bore so as to retain the member in position and to cause theseal to seal between the member and the housing, whereby the sealcontacts the member so as to seal the bore against the passage of fluid,the annular seal being stressed in all lateral and axial directions. 2.A method according to claim 1, wherein the housing is moulded before theseal.
 3. A method according to claim 1, wherein the seal is mouldedaround the member in a first shot; and the housing is moulded around theseal and member in a second shot.
 4. A method according to claim 1,further comprising securing said member to the housing in sealingcontact with the seal.
 5. A method according to claim 1, wherein theseal comprises an O-ring.
 6. A method according to claim 1, wherein theseal contacts part of the housing and the member so as to be restrainedagainst movement in both lateral and both axial directions.
 7. A methodaccording to claim 6, wherein the seal is stressed in at least one ofthe lateral and axial directions.
 8. A method according to claim 1,wherein the seal is located in an annular generally U-shaped recessopening into the housing and contacts opposed sides of the recess andthe side of the recess opposite the member.
 9. A method according toclaim 8, wherein the opposed sides of the recess are substantiallyparallel and orthogonal to the side of the recess opposite the member.10. A method according to claim 1, wherein the material of the housingis different from the material of the seal.
 11. A method according toclaim 1, wherein the seal is chemically bonded to the housing.
 12. Amethod according to claim 1, wherein the member is elongate and sealedin a bore of the housing, further comprising moulding an additional sealinto the bore in a third shot.
 13. A method according to claim 1,wherein the member comprises an electrically conductive pin.
 14. Amethod of manufacturing a gas sensor assembly comprising manufacturing aseal assembly having at least two electrically conductive pins by amethod according to claim 13; and providing gas sensor components in thehousing in electreal contact with the pins.
 15. A method according toclaim 14, wherein the components include sensing and counter electrodes,an intervening electrolyte located within the housing, and a gas accesscontrol member secured to the housing.
 16. A method of manufacturing aseal assembly for a gas sensor assembly, the seal assembly comprising ahousing; and an annular seal supported by the housing and defining abore, the method comprising injection molding the housing about theseal; providing an elongate member including a laterally extendingflange, the flange having a radial barb; inserting the elongate memberinto the bore so that the annular seal contacts a surface of the flangeand an adjacent elongate portion of the member while the radial barbengages the bore so as to retain the member in position and to cause theseal to seal between the member and the housing, whereby the sealcontacts the member so as to seal the bore against the passage of fluid,the annular seal being stressed in all lateral and axial directions. 17.A method according to claim 16, further comprising securing a member tothe housing in sealing contact with the seal.
 18. A method according toclaim 16, wherein the seal comprises an O-ring.
 19. A method accordingto any of claim 16, wherein the seal contacts parts of the housing andthe member so as to be restrained against movement in both lateral andboth axial directions.
 20. A method according to claim 16, wherein theseal is stressed in at least one of the lateral and axial directions.21. A method according to claim 16, wherein the seal is located in anannular, generally U-shaped recess opening into the housing and contactsopposed sides of the recess and the side of the recess opposite themember.
 22. A method according to claim 21, wherein the opposed sides ofthe recess are substantially parallel and orthogonal to the side of therecess opposite the member.
 23. A method according to claim 16, whereinthe material of the housing is different from the material of the seal.24. A method according to claim 16, wherein the seal is chemicallybonded to the housing.
 25. A method according to claim 16, wherein themember is elongate and sealed in a bore of the housing, furthercomprising moulding an additional seal into the bore in a third shot.26. A method according to claim 16, wherein the member comprises anelectrically conductive pin.